Complete re-write of the original Flutter first_app starter app post!

The original post about my Flutter starter app has more than 10k views and the starter app has 159 stars on Github and was listed on AwesomeFlutter. I get hundreds of reads a month, so I figured it was time to update the original post to reflect all the changes to the starter app (and the Flutter project). To keep the links and trackbacks, I updated the post at its original link. Happy fluttering!